Co-sponsorship is sought from the NCI of a Conference on "Regulation of gene expression in development and neoplasia", scheduled by the Kroc Foundation, Santa Ynez, California, for June 3, 4 and 5. In this field of biological research several directions of endeavor can be recognized. In one, model systems have been developed for the study of embryonic gene expression in relation to carcinogenesis in experimental animals and to events of the cell cycle. Another direction is the effort to examine gene products from the very earliest stages of embryogenesis with the concept of the "turning-on" or "off" of sets of genes at each subsequent phase of development. Also, the study of murine teratocarcinoma offers unique opportunities for investigating the interaction of ontogeny and oncogeny. Next, a connection is being sought between viral information in the genome and its expression in development and in neoplasia. Finally, intense contemporary interest exists in elucidating steps in the transcription and translation of genes in eukaryotic organisms. The purpose of the Conference is to bring representative scholars in each of these areas together to establish to what extent these directions may be convergent and productive and to develop ideas for future work.